Recent years have witnessed widely uses of Liquid Crystal Displays (LCDs) in a variety of electronic products, such as mobile phones, notebook PCs, and color TVs, with a thinning trend among displays.
As liquid crystals do not emit light, LCD panels are not able to emit light either. LCD panels, which require lighting sources, therefore, belong to backlight display devices. Liquid crystal displays form images when liquid crystal molecules are twisted after electrodes in the panels are exerted with voltage, thus allowing light beams from the backlight modules to pass through and achieve the effect of light emission. Backlight is an optical module that can provide back light in LCD products. Therefore, the quality of backlight determines important parameters of LCDs, such as brightness of the display screen, uniformity of emergent light, and color gradation. As a matter of fact, the quality of backlight determines glowing effects of LCDs to a great extent.
As backlight of LCDs, Light-Emitting Diodes (LEDs) tend to replace Cold Cathode Fluorescent Lamps (CCFLs) thanks to their advantages of wider color gamut; better color reduction, stronger controllability, longer lifetime, free of mercury vapor or other poisonous gases, etc. Since an LED is a low-voltage non-linear semi-conductor device, the positive voltage thereof will vary along with variation of currents and temperatures. As a result, a driver circuit is needed to guarantee its stable and reliable performance. Therefore, study of LED driver circuits is a major subject for the person skilled in the art.
Currently, in designing an LED backlight driver circuit, especially an LED boost converter, the same ISEN voltage detection point is used for over current protection about circuits in both 2D and 3D display modes. As a matter of fact, the peak values of the inductive currents in the boost circuits in 2D and 3D display modes are different from each other. In addition, due to differences in model designs and LED operation states, Ipk_2D and Ipk_3D can also be different from each other.
However, in a routine design as shown in FIG. 1, the detecting resistor (R1 as shown in FIG. 1) is designed in accordance with the withstand current of the inductor in the 2D display mode. When the 3D display mode is used, since the peak current is changed, the over current protection performed by the ISEN pin detection of the controller (chip GEC 8310) cannot be able to function in the same way as it does in the 2D display mode. Depending on different model designs, element failure or abnormal protection might happen.
Therefore, one of the major problems to be solved in the art is to overcome the above mentioned defects so as to perform the same over current protection for circuits in different display modes against element failure or abnormal protection.